Tire tread buffing apparatus and method

ABSTRACT

A system and method for removing an outer layer of resilient material from an object to achieve a target outer dimension includes performing an initial cut at a cutting depth to remove an outer layer of the material. A parameter indicative of a work input to a cutter that performed the cut is acquired and used to determine the cutting depth that will be used for performing a subsequent cut to remove an additional layer. In this way, subsequent cuts are performed until the target outer dimension is achieved.

BACKGROUND OF THE INVENTION

The invention relates generally to a method and apparatus for makingretreaded tires and, more particularly, to a method and apparatus inwhich the existing tread and material of a tire casing is removed toprovide a tire casing having a desired circumference (or radius) ontowhich a new tread may be installed.

Retreaded tires provide an economical way to gain additional use fromtire casings after the original tread or retread has become worn.According to a conventional method of retreading, sometimes referred toas cold process retreading, worn tire tread and other materials on aused tire are removed to create a buffed, generally smooth, treadlesssurface along the circumference of the tire casing to which a new layerof tread may be bonded.

The tire casing is then typically inspected for injuries, some of whichmay be skived and filled with a repair gum while others may be severeenough to warrant rejection of the tire casing. After completion of theskiving process, the buffed surface may be sprayed with a tire cementthat provides a tacky surface for application of bonding material andnew tread. Next, a layer of cushion gum may be applied to the back,i.e., the inside surface of a new layer of tread, or alternatively, thelayer of cushion gum may be applied directly to the tacky surface on thetire casing. There are other known methods that may eliminate the needfor cement or cushion gum. Conventionally, the cushion gum is a layer ofuncured rubber material. The cushion gum and tread may be applied incombination about the circumference of the tire casing to create aretreaded tire assembly for curing. As an alternative, a length of tiretread may be wrapped around the tire casing with the cushion gum alreadyapplied. The cushion gum may form the bond between the tread and thetire casing during curing.

Conventionally, the buffing of the tire casing is controlled andmanipulated by a human operator of a buffing machine. The buffingmachine includes a rasp that can be applied to the surface of the tireto remove rubber. Because the circumference of a tire casing can moreeasily be measured by the operator, the desired final radius of the tirecasing is typically identified in relation to the final circumference ofthe tire casing. It will be understood that circumferential measurementsin this application are equivalent to radial/diameter measurements inthat they are related by π. As the final desired circumferenceapproaches, the operator may take a measuring device (e.g. a tapemeasure) and wrap it around the circumference of the casing to obtain ameasurement and guess at the depth of each subsequent cut. Thisimprecise and error ridden process is time consuming and often resultsin a tire casing with a radius or circumference that does notsubstantially meet the final desired circumference.

One manner to reach the final circumference is to move the rasp into thedesired position matching the final desired radius (or circumference)and keep repeating passes over the casing until there is no rubber beingremoved. This is very inefficient and unsatisfactory, and is thus nottypically practiced.

There are a multitude of problems that may result from the imprecisionof uncontrolled buffing of the tire as is typically practiced throughthe operator guessing the depth of final cuts or intentionallypermitting imprecision. The treads on the tires are sometimes in theorder of an inch or so in depth. On certain vehicles, two tires may bemounted next to each other on the same axle. If the radius of the tiresis not substantially the same, a condition commonly referred to asscrubbing may occur. Such condition may derive from the radius of eachfinal tire being different and, consequently, the velocity at the outersurface of the tire having a larger radius will tend to be larger thanthat of the tire having the smaller radius. The difference in velocity,given that the tires are mounted on the same axis, can generate frictionin the tires at their outer surfaces, which tends to wear or scrubmaterial from the tires in undesirable manners.

Another problem, among many others, generated by imprecision in arrivingto the final circumference of a tire casing is that the tread to beapplied may not match the casing, e.g., it may be too short or too long.In some instances, the tire tread is pre-cut to length before the tirecasing is prepared while in other cases, the tread needs to be cut sothat the tread pattern is continuous over the splice. In such instances,the predetermined length of the tire tread is expected to match thecircumference of the buffed tire casing. When the circumference of thetire casing does not correlate properly with the predetermined length ofthe tread, which can occur through variability in the final outercircumference of the buffed tire casing, the tread will not match. Inany event, the failure to substantially match final circumference of thetire casing to the target circumference of the tire casing and thepredetermined length of the tread to be bonded to the tire casing canresult in undesirable performance deficiencies.

A further undesirable problem with prior tire buffing has been thatthere can be delays and time inefficiencies as the operators attempt toexperiment with the placement and operation of the rasp as rubber isbeing removed from the tire. Such time inefficiency and placement errorsagain result in undesirable performance deficiencies.

All of the noted problems and undesirable deficiencies are exacerbatedfurther by the variability in the condition of incoming worn tires (ortire casings) that are commonly experienced. Incoming worn tires or tirecasings often have rubber that is of differing characteristics dependingon the environmental conditions to which they have been subjected inservice. For example, tire casings that have been subjected to sustainedheat might be more brittle than other tire casings that are younger andhave not been subjected to heat. Some tire casings might have beenstored for long periods in warehouses. Such and other historicalcircumstances of the incoming tire casings result in a significantlyvariable rubber product. Consequently, each buffing operation fordifferent tires proceeds with different efficiencies andcharacteristics. Such differences further contribute to the final casingbeing variable and resulting in the noted problems.

BRIEF SUMMARY OF THE DISCLOSURE AND EXAMPLE EMBODIMENTS

The invention provides an apparatus and method for processing tirecasings, which are at an unknown and/or inconsistent material condition,to produce buffed tire casings having an outer circumference that isappropriately sized for subsequent retreading operations. The apparatusand methods described herein provide for automated buffing of a tirecasing which is more expedient, consistent, and accurate.

It has been discovered that the final circumference (or radius) of atire casing may be obtained through automated buffing that adjusts, insubstantially real time, for variations that may occur as tire casingsof varying conditions are processed. The apparatus and method providefor monitoring electrical signals that are indicative of the processingconditions of the tire casing as buffing proceeds. The electricalsignals are then correlated to an offset to facilitate improved cuttingand buffing to consistently and substantially reach a target outercircumference or radius, which is a significant improvement over priorprocesses that were inefficient and inaccurate.

When processing a tire casing to remove rubber, it has been discoveredthat a rasp (which refers herein to any rubber removing device, e.g.rasp, cutter, etc.) locally deforms the tire to the cutting depth of therasp around the contact area. The conditions of the rubber and thedeformation contribute to a cut that often does not remove all of therubber engaging by the cutter at the cutting dept in a single pass, butleaves behind a certain amount of rubber that depends on processing andtire conditions. The remaining rubber may accumulate (or become storedrubber) as repetitive passes are made at iterative cutting depths,especially if the passes are incrementally deeper in equal in-feed ratesin the radial direction. In other words, as may be the case, a rasp maybe moved inwardly in equal increments to a target circumference orradius after each pass. There are many patterns of passes that may bemade including ones where the rasp is applied in locations starting atone side of the tire and moving to the other side of the tire, therebymaking an arced pass across the tire. As the rubber accumulates witheach pass, the difference between the outer circumference of the tireand the position of the rasp increases.

By monitoring electrical signals indicative of the processing of thetire and analyzing such signals, the amount of offset between theresulting diameter and the position of the rasp may be determined as thefinal pass occurs or approaches. With such information, the final passmay be adjusted so that the position of the rasp is set based on thecalculated resulting outer circumference. In many cases, especiallywhere there is an accumulation of stored rubber, the radial position ofthe rasp will be closer to the central axis of rotation than the targetouter circumference or radius would otherwise indicate. This providesfor better control over obtaining the final outer circumference andpermits for better precision resulting in a casing that substantiallymeets the target circumference or radius of the casing.

In certain embodiments of the invention, the electrical signals that aremonitored are electrical signals relating to the motors driving eitheror both of the rasp and tire. The power or work drawn by such devices isrelated to the amount of rubber material that is being accumulated orstored through each pass in a cumulative manner. Through such signals,the positioning of the rasp in the final passes may be adjusted so thatthe resulting circumference or radius of the tire casing is reached in amore efficient manner.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of a tire buffing system in accordance withthe disclosure.

FIG. 2 is a detail view of the buffing system of FIG. 1.

FIG. 3 is a functional diagram of a controller in accordance with thedisclosure.

FIG. 4 is a functional diagram of a material storage estimation functionin accordance with the disclosure.

FIG. 5 is a flowchart for a method in accordance with the disclosure.

DETAILED DESCRIPTION OF THE INVENTION AND EXAMPLE EMBODIMENTS

A buffing machine 100 having a tire 102 mounted on a rotating rim 104 isshown schematically in FIG. 1. As shown, the machine 100 may be astandalone, dedicated machine for buffing tires prior to a retreadingoperation, or may alternatively be part of a retreading machine that canperform other operations, such as installing a new tread onto thecasing.

In the illustrated example embodiment, the rim 104 and tire 102 rotateat a constant angular rate of rotation during operation, for example,60-90 revolutions per minute (RPM), but may also rotate at a variablespeed. An electric motor 106 is connected to a hub 108 of the rim 104 toprovide the rotation of the tire 102, but any other type of rotaryactuator may be used, such as hydraulically or pneumatically poweredmotors, or even mechanical arrangements providing a rotating output. Asshown, the hub 108 includes timing features that are picked up by anangular displacement encoder 110 associated with the machine 100. Acontrol signal of the motor 106 may be provided by an electroniccontroller 112 via a motor control conduit 114, while informationindicative of the rotation of the hub 108 may be provided to thecontroller 112 by the encoder 110 via a tire rotation informationconduit 116.

The machine 100 further includes a buffing tool or rasp 118. The rasp118 may be any device capable of cutting material from the rotating tire102. In an illustrated example embodiment, the rasp 118, which is shownin more detail in FIG. 2, includes a laminated steel drum having sawteeth 120 arranged around its outer cylindrical surface. The illustratedexample rasp 118 has a length of about 4 inches (10.2 cm) and a diameterof about 8 inches (20.4 cm).

Although many configurations are possible, the rasp 118 is connected tothe machine 100 at the end of an arm 122. The position of the arm 122and of the rasp 118 relative to the tire 102 can be adjusted by a raspactuator 124. The rasp actuator positions the rasp head to sweep acircular arc across the face of the tire at a defined radius. A forcethus derived is caused by the interference between the rasp face and thecircumference of the tire being buffed. There are other arrangements ofthe arm, actuator, and other parts of the cutting assembly that areknown in the art and incorporated herein. This pressing or normal forceeffects removal of material from the tire 102 and is carried out inresponse to command signals provided by the electronic controller 112via a rasp actuator control conduit 125. As best shown in FIG. 2, theouter circumference 126 is illustrated by dashed line. In that samefigure, the cutting depth 128, which is located radially inward from theouter circumference 126 relative to a center of the tire 102, is shownin dash-dot-dashed line.

During a cutting operation, the rasp 118 is driven by a rasp motor 130in a counter-rotational direction relative to the tire 102. The motor130 is controlled and monitored by the electronic controller 112 througha motor control conduit 131. When the rasp 118 is in position at thecutting depth 128 and the motor 130 is operating, material is removedfrom the outer portion of the tire 102 as the teeth 120 of the rasp 118are pressed against the outer circumference 126.

Information indicative of the cutting depth 128 is provided to theelectronic controller 112 by a position sensor 132. In the illustratedexample embodiment, the position sensor 132 is associated with the arm122 to provide information indicative of the absolute radial position ofthe rasp 118 relative to the centerpoint of the hub 108, but otherarrangements may be used, such arrangements being known to practitionersin the art. Information from the position sensor 132 is provided to theelectronic controller 112 via a rasp position information conduit 134.In one embodiment, measurements of the casing circumference are providedto the electronic controller 112 by a measurement wheel 136. Themeasurement wheel 136 of the illustrated example embodiment isassociated with an encoder 138 that is connected to the electroniccontroller 112 via a measurement information conduit 140. Themeasurement wheel 136 is free rotating and, when it is placed in contactwith outer circumference of the tire 102, rotates such that the encoder138 can provide information indicative of the outer circumference of thetire 102 when the tire performs a full rotation. In an alternativeembodiment, the encoder 138 may be associated with the rasp 118 andprovide a measurement to the electronic controller 112 by placement ofthe rasp 118, which in this instance is unpowered and free to rotate, incontact with the tire 102.

The machine 100 may further include other components and systems. Forexample, the machine 100 may include computer networking components andsystems (not shown) enabling its control from a remote or otherwisecentral location. In the illustrated example embodiment, the machine 100includes an operator interface 142 that enables local operation of themachine 100. The operator interface 142 includes a display 144 and akeypad 146 that can be used during operation to display the status ofthe buffing process as well as to input information into the electroniccontroller, such as the type of tire being processed, the desiredcircumferential dimension sought to be achieved, and others. The two-waycommunication of information between the electronic controller 112 andthe operator interface 142 is conducted via an operator informationconduit 148.

During a cutting pass, the rasp 118 is set to the cutting depth 128 andresiliently compresses the material of the tire in the region of contact150 between the rasp 118 and the outer circumference 126. Thecompression pushes the material along the outer portion of the casingagainst the teeth 120 of the rasp 118. This compressive force is notconstant, but rather changes depending on the angular location along theregion of contact 150 relative to the centerpoint of the rasp. The forcereaches its maximum magnitude along a line connecting the center pointsof the rasp 118 and the tire 102. Although the teeth 120 are able to ripmaterial away from the tire 102, the amount of material thus removeddepends on various parameters and factors, such as the resiliency of therubber, the sharpness of the teeth, the aggressiveness of the cut depth,the rate of rotation of the tire and rasp, and others.

As shown in FIG. 2, the rasp 118 does not remove the entire layer ofmaterial disposed between the outer circumference 126 and the cuttingdepth 128 in a single pass, which leaves a layer of stored material 152having a thickness 153 on the outer portion of the tire 102. After eachpass of the rasp 118, the new outer circumference 154 of the tire 102will be radially located between the previous outer circumference 126and the cutting depth 128. The radial distance of the cutting depth 128,which is augmented by the thickness 153 of the stored layer 152 in theradial direction, will determine the radial location of the new outercircumference 154 of the tire 102. The layer of material that wasremoved from the tire 102 has a thickness 156 in the radial direction.

The ratio of the thickness of the layer of removed material 156 relativeto that of stored material 153 for a given cutting depth 128 depends ona multitude of parameters, such as the temperature and aging of the tirematerial, the shape, arrangement, and sharpness of the teeth 120, therotational speed of the rasp relative to the tire, the distribution ofrubber across the width of the tread (for tires worn unevenly), andothers. The amount of offset or stored material may be monitored basedon correlations of work expended during the cutting operation. Thecorrelations can be determined empirically, for example, based onrunning a group of tires through the process and then collecting theactual outer circumference as electrical signals are monitored.Depending on the particular setup of the machine, such empirical datamay vary. Therefore, in the context of this invention, the best methodof providing such data is to also perform certain machine setup tasksfor each particular machine in the manner described herein.

The estimation of the thickness 153 of the stored material layer 152 maybe further corrected for machine specific factors, such as the length ofservice of the rasp. When implemented in the machine 100, thecorrelations can be distilled into individual equations or equation setsthat include experimentally-determined factors applied to variablesmeasured from the system using various sensors.

In accordance with the foregoing, a block diagram of the electroniccontroller 112 is shown in FIG. 3. The electronic controller may be asingle controller or may include more than one controller disposed tocontrol various functions and/or features of a machine. For example, amaster controller, used to control the overall operation and function ofthe machine, may be cooperatively implemented with one or more motorcontrollers. In this embodiment, the term “controller” is meant toinclude one, two, or more controllers that may be associated with themachine 100 and that may cooperate in controlling various functions andoperations of the machine 100 (FIG. 1). The controller's operation isshown in FIG. 3 to include various discrete operations for illustrativepurposes only, may be implemented in hardware and/or software withoutregard to the discrete operations shown. Accordingly, various interfacesof the controller are described relative to components of the buffingmachine 100 (FIG. 1) shown in the block diagram of FIG. 3. Suchinterfaces are not intended to limit the type and number of componentsthat are connected, nor the number of controllers that are described.

As shown, and in ongoing reference to the components shown in FIG. 1,the electronic controller 112 is disposed to receive various inputs fromthe various sensors of the machine 100. In this way, the measurementinformation conduit 140 providing information indicative of the measuredcircumference of the tire is connected to a transfer function 302 thatprovides an initial or current circumference (CC) 304 of the tire 102.In a similar fashion, the rasp motor control conduit 131 is connected toa transfer function 306 that provides an average rasp current (ARC) 308,which is indicative of the power consumed by the rasp 118 (FIG. 1)during operation. The average rasp current (ARC) 308 may be monitoredduring the performance of a cut as well as when the rasp is idle. Avalue indicative of the current 310 drawn by the electric motor 106driving the rim 104 is provided by a transfer function 312, whichreceives information from the rim motor control conduit 114.

The controller 112 is further disposed to receive information indicativeof the rotational position of the rim 104 by a signal received via therim position information conduit 116 from the rim encoder 110. In theillustrated example embodiment, the rim encoder 110 is a hall effectsensor, but any other appropriate type of contacting or non-contactingsensors may be used. The rotational position 317 of the rim 104 isprovided to a rotation counter 314 via a transfer function 316. Finally,in the example embodiment illustrated, the controller 112 is disposed toreceive a signal indicative of the actual position of the rasp 118relative to the rim 104. The position of the rasp 118, which isindicative of the cutting depth, is provided as a signal from the armposition sensor 132. The arm position sensor 132 is connected to thecontroller 112 via the arm position information conduit 134, whichprovides information indicative of the actual cutting depth 319 of therasp 118 via a transfer function 318.

Information provided by various sensors of the machine is used by theelectronic controller 112 to calculate or otherwise determine the numberof cuts, as well as the appropriate cutting depth for each of those cutson the tread portion of the tire 102 that will yield a casing having adesired target circumference. These determinations are essentially basedon the calculation or estimation of the amount of material stored in thetire 102 after each cut. In the illustrated example embodiment, thecalculation or estimation of the material stored is based on anestimation of the material removed by each cut, and on the cutting depthused for that cut. The calculation or estimation of the material storedor removed by each cut, which can be used to determine subsequent cutsand subsequent cutting depths, as is described in more detail below, isperformed in estimation function 320.

The estimation function 320 is arranged to receive and processinformation indicative of various functional parameters of the machine100. In the illustrated example embodiment, the estimation function 320receives required and optional signal inputs. Thus, the circumferencevalue 304, the current consumption of the rasp and rim motors 308 and310, the rotational position of the rim 317, the rotational count 314 ofthe rim, and the actual cutting depth of the rasp 319, are provided tothe estimation function 320. Certain of these values, such as the powerconsumption of the rasp motor, have a direct correlation to the amountof material removed by each cut, while other values, such as the currentconsumption of the rim motor or tire drive motor (TDC) 310, areoptional, but may be similarly indicative. Such and other optionalvalues may improve the accuracy of the estimation of the amount ofmaterial stored on the tire during processing and/or improve therobustness of the system under changing conditions, but can be omittedand still maintain acceptable system performance. In the illustratedexample system, the estimation function 320 is arranged to calculate ordetermine the number of cuts and the cutting depth of each cut that willproduce a tire casing at a desired circumference.

In the illustrated example embodiment, the estimation function 320 hasaccess to process-specific constants or parameters, which are stored andretrieved from a memory device 322. The memory device 322 may be anyappropriate type of electronic information storage and retrieval device.The electronic information stored and retrieved in the memory device 322may include a library of processing information, equation factors,desired circumference values, historical information indicative of thewear of the rasp and other machine components, and other information.Moreover, the memory device 322 can contain information relevant to on aparticular type of tire being processed, as well as other informationrelevant to machine components, such as the used or remaining life ofthe rasp teeth, statistical information on the number of cyclesperformed by the machine, productivity data such as the average cycletime of the machine, tracking information on the specific tiresprocessed by the machine, log data relative to each tire, and so forth.Such specific information is collected by repetitive processing of thetires and varies based upon the exact type of machine being employed topractice the disclosed method and apparatus. Specific information oneach tire mounted to the machine, as well as retrieval of informationfrom the memory device 322, may be accomplished by an appropriateconnection to a computer and/or connection to the operator interface142. Thus, an operator may place the machine into an appropriateoperating mode after a tire has been mounted in the machine by simplyselecting the type of tire that is mounted before initiating theprocessing operation. During the operation, the operator may monitor themachine's progress until the process is complete, and additionally usethe display to verify that the buffed casing has a circumference thatsubstantially matches the target circumference for the tire casing beingprocessed.

A flow diagram showing the various variables used for the calculationsand processing occurring within the estimation function 320 is shown inFIG. 4. The variables illustrated include external variables that areprovided to the system, variables developed internally to the systembased on the external inputs and other parameters, as well as constantsthat are provided to the system during initial setup such as historicalvalues and other constants, as is provided in more detail below. Thesevariables and constants are used to perform calculations that generateparameters used to control the operation of the buffing machine duringthe cutting operation. Although a specific set of variables is discussedherein, and specific implementations for achieving the contemplatedfunction are presented, other implementations are possible that canachieve the same or similar results as those disclosed in theillustrated example embodiment.

The estimation function 320 includes a calculation of the efficiency ofthe cutter (CEF) 402, which represents the ability of the cutter toefficiently remove material from the outer portion of the tire. Thecalculation of CEF 402 may be based on experimental performance tests ofrasps operating at various wear conditions. In the illustrated exampleembodiment, the calculation of CEF 402 is based on the cut depth (CD)319 of the previous pass, which is provided externally, and on thevolume of material removed over the life of the rasp (Vrasp) 404, whichis calculated internally, and on historical data provided by the memorydevice 322 (FIG. 3). The historical data provided by the memory device322 may include information on the number of processing cycles that aparticular rasp has undergone, the number of tires processed over thelife of a particular rasp 406, and/or a number of tires processed sincethe rasp was sharpened 408, all of which are retrieved from the memorydevice 322.

In the illustrated example embodiment, the rasp actuator is capable ofaggressively driving the rasp motor beyond its maximum normal drivingcapacity, thus achieving a more aggressive cut. This function canoptionally be accomplished by use of a dynamically controlled drivefeature applied to the rasp actuator, the operation of which iscontrolled based on rasp current and loading set points, for example, arasp set point (RSP) 410 and a rasp break point (RBP) 412. Both theseparameters can be expressed as a percentage of the rasp rated motorcurrent. The set point 410 determines the maximum end of overload thatis acceptable, and the break point 412 represents a motor overloadbeyond which driving of the rasp actuator is scaled down, for example,to 5% of its programmed speed when the rasp current reaches the RSP, toavoid damage to the motor. These two overdrive parameters can becombined, for example, in a model, to provide the CEF 402, which is usedin other calculations.

The CEF 402 is combined with other variables in a set of materialdisposition calculations 414, which are shown collectively in a singlefunctional block. The material disposition calculations 414 comprisevarious calculations or other processes that determine by anyappropriate method various parameters, such as the amount of materialthat was removed from the tire (Vtire) 416A by a previous pass of therasp, the amount of material stored on the tire (Storage) 418A by theprevious pass of the rasp, the cut depth (CD) 319A that should be usedin a subsequent pass, and others. These determinations may be performedusing numerical manipulations, system modeling equations, interpolationof data based on tabulated information, and other types of dataprocessing and determination.

In one example embodiment, the material disposition calculations 414 arebased on a correlation between the energy input to the system as itrelates to the amount of material removed from the tire by the buffingprocess. In the machine illustrated in FIG. 1, for example, energy isinput to the tire buffing system through the power consumed by the raspmotor and/or the rim motor. Insofar as the energy or power input to thesystem can be determined by monitoring the electrical current input toeither or both of these motors, a correlation to the material removedfrom the tire during each cut can be experimentally determined.Thereafter, by determining the amount of material removed, inconjunction with information indicating the depth of each cut performed,the amount of material stored onto the tire can be determined by acorrelation of the stored material amount to the energy or power inputto the system. It will be appreciated that voltage and other electricalsignals may be monitored to accumulate information that is indicative ofthe same thing.

In that same embodiment, an algebraic relationship may be definedbetween the current input to, for example, the rasp motor, and thematerial storage on the tire. Such algebraic relationship may take onany form that approximates the dynamic behavior of the tire buffingprocess, such as linear, exponential, or any other appropriateapproximation. One example of such a linear form of the algebraicrelationship, which was successfully tested on the machine 100 (FIG. 1)to remove the tread portion of a tire, is shown in Equation 1 below:(Storage Change)=1.2878*ARC−65+(Storage Adjustment)  Equation 1where “Storage Change” represents an amount of material removed from thetire, “ARC” represents the average current input to the rasp motor, and“Storage Adjustment” represents 65% of the Storage Change calculated ina previous cut. The stored material amount in a previous cut is thuscompounded with the storage of material in a subsequent cut. Althoughthe experiment was successful in yielding reasonable results incalculating the amount of material removed from the tire with each pass,the linear relationship that was used as represented in Equation 1 canbe improved by changing its form to add additional variables that havebeen found to compensate for other physical and machine parameterspresent during the cutting process. In this way, the accuracy of theestimation of the amount of material stored on the tire can be improved.

Turning now to the example embodiment shown in FIG. 4, a more developedform of the equation is illustrated. In this embodiment, additionalvariables that compensate for various other factors affecting theaccuracy of the estimation of the amount of material stored on the tireare included, which are represented by the input variables to thematerial disposition calculations 414. As shown, a desired or programmedtarget circumference (PC) 420, a maximum expected material storage value422, which is a threshold value representing the worst-case storagecondition expected, and a previous value of the rasp current (PRC) 424,are provided from the memory device 322 (FIG. 3) to the materialdisposition calculation block 414 as internal variables. Calculatedparameters are also provided as internal variables, such as a materialstorage condition existing after the last pass of the rasp was performed(Storage) 418, as well as the total volume or amount of material thathas been removed at any given time from the tire being processed (Vtire)428, both of which are calculated and their values updated in real time,are provided as internal variables. External variables include the raspmotor current 308, which is acquired and stored when the rasp is notcutting and expressed as a rasp idle current (RIC) 422, the average raspcurrent (ARC) 308 that is acquired during a cutting operation, and thetire drive or rim drive current (TDC) 426.

It should be appreciated that the material estimation function 320continuously processes various parameters, and updates the three outputparameters of the material disposition calculations 414 at eachprocessing cycle of the electronic controller 112. In one embodiment,various calculations are repeated for each cutting cycle. A samplecalculation for determining the change in storage material after eachcutting pass of the rasp, which is conducted while the currentcircumference (CC) 304 is greater than the target or programmedcircumference (PC) 420, is provided in Equation 2 below. Equation 2 asshown below represents the tire buffing process that is modeled for anestimation of the amount of material stored with each cutting pass ofthe rasp:StorageChange=(CEF)*(A*URC+B*e^(−b*URC)+C*e^(c*URC)+D*e^(d*Vtire)+F*e^(f*Vtire)+G*e^(g*RBP)+H*e^(h*RBP)+(I*e^(i*RBP)+J*e^(j*RSP)+K*e^(k*RSP)+M*e^(m*RSP)+N*e^(n*PRC)+O*e^(o*CD)+R*e^(r*CD))  Equation2where “A” through “R” and “b” through “r” are factors that areexperimentally determined, and where the system variables used in theequation, as those variables are shown and previously described aboverelative to FIG. 4, are provided in Table 1 below:

TABLE 1 Variable Parameter Type CEF Cutter Efficiency Calculated URCUseful Rasp Current Calculated Vtire Volume of material removed fromCalculated, set to 0 at tire being processed initiation of process RBPRasp Break Point Constant (%) RSP Rasp Set Point Constant (%) PRCPrevious Rasp Current Historical/variable CD Cut DepthHistorical/variable

It should be appreciated that fewer, more, or different variables thanthe those shown in Equation 2 may be used to model the tire buffingprocess. For example, terms containing the tire drive current (TDC) 310can be added to the equation as compensation for energy losses in thebuffing system. Such additional terms may also be used to perform sanitychecking of the values provided by the various sensors, for example, thecurrent draw of the rasp motor, and/or for setting limits to thevariables used in the calculations.

In Equation 2 above, the cut depth (CD) for each cutting pass of therasp is selected by the system as the lesser of either a programmed orpredetermined cut depth (PCD), which is a predetermined incrementalcutting depth, for example, 0.069 inches (1.75 mm), or a cut depthdetermined as a function of the current circumference of the tire (CC),the target or programmed circumference (PC), and the amount of materialstorage on the tire, as provided in Equation 3 below:CD=Min[PCD,(CC−PC−Storage)/2*π)]  Equation 3Further, the useful rasp current appearing in Equation 2 above is acalculated parameter that is determined based on the average raspcurrent (ARC) acquired by the system, minus the rasp current at idle(RIC), as provided in Equation 4 below:URC=ARC−RIC  Equation 4In the illustrated example embodiment, the idle current of the raspmotor (RIC) when no cutting is taking place is measured at each machinestartup and stored in the memory 322 (FIG. 3) as a constant value whilethe machine is operating.

The volume of material removed from a tire being processed (Vtire), aswell as the volume of material removed during the life of the particularrasp being employed (Vrasp), are incremented when material is removedduring each cutting pass of the rasp. These calculations are similar andare shown in, respectively, Equations 5 and 6 below:Vtire_(n+1) =Vtire_(n)+(CD*Tread_Width*CC)  Equation 5Vrasp_(n+1) =Vrasp_(n)+(CD*Tread_Width*CC)  Equation 6where “Vtire_(n+1)” and “Vrasp_(n+1)” are incrementally increasedestimations of the volume of material removed by a last cutting pass ofthe rasp over the tire, “Vtire_(n)” and “Vrasp_(n)” are thecorresponding values of volume of material removed by the cutting passimmediately preceding the last cutting pass, “CD” and “CC” are,respectively, the cutting depth and current circumference of the tire aspreviously described, and “Tread_Width” is a constant that is equal tothe width of the tread of the particular type of tire being processed.The width of the tread as well as other tire-specific parameters can beentered by the operator and/or retrieved from the memory device 322(FIG. 3) before each cutting operation as was previously described.

Having described the calculations and processes for determining theincremental change in volume or amount of material stored onto the tireby each cutting pass of the rasp, a total amount of material stored onthe tire (Storage) can be determined as a non-negative integral value ofall incremental storage changes accumulated on the tire being processed,as provided in Equation 7 below:Storage_(n+1)=Min[Max_Storage,Max(0,Storage_(n)+StorageChange_(n+1))]  Equation 7where “n+1” refers to the last cutting pass performed on the tire, “n”refers to the cut preceding the last cut, and “Max_Storage” is aconstant representing the maximum storage volume or amount of materialthat can accumulate on any particular tire type in a single cut. Thisparameter can be retrieved from the memory device 322 (FIG. 3) and canbe determined experimentally by, for example, performing a sample cut ona tire using a rasp that has worn to the end of its useful service.Having determined the amount of Storage, the cutting depth for asubsequent cut is determined as provided in Equation 3 above for eachcutting pass.

In another example aspect, the disclosure provides a method for buffingcasings to a correct target dimension. A flowchart for a method ofpreparing a tire for application of new tread by removing the existingtread, a process commonly referred to as buffing, is shown in FIG. 5.The method may be part of a tire processing system, which includes amachine operating in concert with an electronic controller, or may be astandalone process. The machine, along with any controllers that may beintegrated or cooperating remotely therewith, are collectively referredto in the discussion that follows as a tire processing system, system,or process, for simplicity.

In reference to FIG. 5, the process includes an optional determinationof the type or model of tire to be processed at 502. This informationmay be automatically acquired by an electronic system, for example, byscanning a barcode on the tire or on a label previously placed on thetire, or it may alternatively be manually input into the system by anoperator. This determination is optional because it depends on thevarious types of tires a process may be used on. In this way, a processintended for processing a single type or a single family of tire modelsmay not require this determination as the various constants used by thesystem will not change. Moreover, a well-developed system may bearranged to automatically account for or measure any parameters that arespecific to a particular tire type and account for any changesautomatically. Along these same lines, the process may further includean optional determination of the desired circumference of the finishedcasing. This target or programmed circumference (PC) of the casing willtypically depend on the type of tire being processed and may bedetermined by the system based on the type of tire being processed or,alternatively, based on an input by the operator.

After the desired circumference of the casing has been determined, theoriginal or current circumference (CC) of the tire is measured at 504.The measurement of the tire circumference, which includes the tread tobe removed, may be measured by any appropriate mode of measurement, forexample, by use of the rasp 118 or the measurement wheel 136 asdiscussed relative to FIG. 1, and represents a baseline dimension of theworn tire that is an indication of the amount of material that should beremoved to achieve a desired casing dimension. In the case of the rasp118, the rasp is moved closer to the axis of rotation until it contactsthe tire and begins to rotate. The radial distance at which the rasp 118begins to rotate may be equated to the outer circumference or radius ofthe tire to be processed. In one embodiment, such measurement may onlybe performed once before any cutting is performed on the tire. In otherembodiments, the measurement may be taken multiple times or at differentlocations across the arch of the wheel from side to side. Thereafter,during the cutting operation, the circumference may be estimated basedon the estimated amount of material removed from the tread portion ofthe tire substantially in real time. In alternative embodiments,however, the actual circumference of the tire may be monitored aftereach cutting pass, and the information thus acquired may be used incontrolling subsequent cutting processes or, alternatively, in adjustingthe accuracy of the material disposition estimations performed by thesystem.

Having determined the desired and actual dimensions of the tire casing,the system may optionally determine the amount of material that isrequired to be removed or buffed from the tire at 506. The determinationat 506 is optional and may be based on the difference in diameter orcircumferential length between the original dimension of the tire andthe desired dimension of the casing that will result. The amount ofmaterial that should be removed, thus estimated, may be expressed in anysuitable units, for example, volume, weight, mass, or it mayalternatively be expressed as a thickness of a layer that should beremoved from the outer portion of the tire. In alternative embodiments,the system may determine whether additional cuts should be performed orwhether the target circumference has been reached by comparing thedifference between the initial measured circumference and the desiredcircumference with an estimated thickness of material removed from thetire, which is reset for each tire and is incremented with each cuttingpass on a particular tire.

Having determined the target parameters for processing the tire, thesystem determines whether the target circumference of the tire has beenachieved or, stated differently, whether an amount of material requiringremoval is still present on the tire at 508. As can be appreciated, thedetermination at 508 initiates the cutting process and causes successivecuts to be performed while material to be removed is present on the tireor casing.

When the system determines that material to be removed is present, adetermination of the cutting depth is performed at 510, and a cut isperformed at the predetermined cutting depth at 512. The cutting depthdetermined at 510 may represent the depth to which a rasp may be placedin contact with the outer portion of the tire. For example, as shown inFIGS. 1 and 2, the cutting depth is the depth relative to the outercircumference of the tire 102 at which the rasp 118 is placed by therasp arm 122. When determining an appropriate cutting depth while thematerial to be removed is above a threshold, the system may advance therasp in predetermined increments, for example, 0.069 inches (1.75 mm.).This incremental increase may be repeated for each cutting cycle orcutting pass while the material layer to be removed is at least equal toor greater than a threshold thickness.

When the remaining material layer to be removed is less than thethreshold thickness, the system may determine an appropriate cuttingdepth that will provide one or more finishing cuts on the casing. Inother words, the system may perform one or more final, finishing cut(s)that will yield the desired or target circumference of the casing. Thedepth of such finishing cuts is advantageously compensated based on theamount of material stored on the tire after one or more preceding cutshave been performed. Thus, in the preferred embodiment, the rasp ismoved equal incremental distances from the original outer circumferenceor radius until it nears the target circumference or radius. The lastpass, which often requires a cut to be performed at a depth that is lessthan the incremental depth increases, may still be greater than thedistance that would equate to the final target circumference or radius.By moving to a cut that is deeper than necessary, the offset generatedby the accumulated storage of rubber may be accounted for, andefficiency and greater accuracy may be obtained.

Following each cut, the system may estimate the amount of materialstored by that cut at 514. As was previously described, the materialstored refers to the layer of material that elastically recovers afterthe rasp has passed. Although the rasp is able to remove material fromthe outer portion of the tire due to the compressive force applied tothe material under the rasp, this compressive force is inadequate tocause cutting of the material beyond a certain depth in a single pass.Thus, the outer portion of the material experiencing larger compressiveforces is removed by the rasp, and an inner portion, which is stillwithin the cutting depth of the rasp, is left on the tire.

The estimation of the amount of material stored on the tire in theillustrated example embodiment is performed based on the work done toremove the material that was removed from the tire. In one embodiment,this work may be compared with a theoretical work that would have beenrequired to remove the entire layer of material encompassed by thecutting depth of the rasp. In the illustrated example embodiment, thework input to the cutter at each pass, i.e. the work required by therasp to remove a certain amount of material from a tire, is correlatedto the amount of material thus removed. This correlation, which candepend on a multitude of physical factors, can be determinedexperimentally for any given type or model of tire.

More specifically, the work input to the rasp during a single cuttingpass may be determined by measurement of the current input to anelectric motor driving the rasp. In one embodiment, the work input tothe rasp during the cutting operation can be compared and expressed as apercentage of the total work that would have been required to remove theentire layer of material within the cutting depth. The percentage ofactual work in relation to the total work in that embodiment can be thencorrelated to an amount of material that was removed by the measuredwork of the rasp. For example, if a pass of the rasp is determined tohave consumed 40% of the work that would have been required to removethe entire layer of material within the cutting depth, the remaining 60%of the work represents the amount of material stored on the tire.

The system can further estimate the total amount of material stored onthe tire, or the amount of material that still needs to be removed fromthe tire to achieve the target circumference at 516. The systemcalculates an incremental amount of material removed by each cut at 518.Having determined the incremental amount of material removed by each cutat 518, the system may integrate or calculate the aggregate materialremoved from each tire at 520, and return to the determination at 508.As stated above, the process-loop around the determination at 508 willrepeat as long as material to be removed is present on the tire. After afinal cut is performed and the system determines that the aggregate sumof all incremental material removal cuts is within a predetermined rangeof the target material removal, the determination at 508 will turn to anaffirmative outcome and the process will continue with optional steps522, 524 before terminating. In the illustrated example embodiment,optional step 522 includes a final measurement of the circumference ofthe casing to validate the circumference and flag the part as acceptedwhen the circumference corresponds to the target value or reject thecasing if the circumference is out of specification. The optional step524 includes logging of various parameters of the casing in the machinefor later retrieval and analysis by the operator.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

The invention claimed is:
 1. A method for manufacturing a retreaded tireincluding buffing a tire casing to be retreaded, such method comprising:mounting the tire casing to be retreaded so that it may be rotated abouta central axis; taking an outer measurement indicative of the distancefrom the central axis to an outer surface of the tire casing; performingiterative cuts to remove rubber from the tire casing to be retreadedusing a cutting device; acquiring electrical signals corresponding to anamount of electrical work that has been expended by the cutting devicethrough the iterative cuts; estimating an amount of material removedfrom the tire casing through the iterative cuts based on the amount ofelectrical work; between each iterative cut, using the electricalsignals to estimate an amount of material stored by the previous cut,the material stored defined as the difference between a total amount ofmaterial made available for removal by moving to a cutting depth of theprevious cut and an amount of material actually removed by the previouscut; determining a target outer dimension of the tire casing afterbuffing, such target outer dimension indicative of a desired distancefrom the central axis to the outer surface of the tire casing;determining an offset, based on the amount of material removed throughthe iterative cuts, for a final cut made on the tire casing to beretreaded, such offset being indicative of an amount of rubber not beingremoved by prior iterative cuts because of elastic recovery of a rubbermaterial of the tire casing after the cutting device has passed over therubber material; performing the final cut on the tire casing where theoffset is applied to adjust a radial position of the final cut so thatit is nearer to the central axis than the target outer dimension, suchoffset yielding an achieved outer dimension of the tire casing thatsubstantially corresponds to the target dimension; applying and curing atread to the tire casing in a manner to attach such tread and generate aretreaded tire.
 2. The method of claim 1, wherein the outer measurementof the tire is at least one of a radial and a circumferentialmeasurement.
 3. The method of claim 1, wherein the iterative cuts areperformed by a cutter and wherein the offset is further determined basedon an estimated wear of the cutter.
 4. The method of claim 1, furthercomprising estimating an amount of material to be removed from the tirecasing based on the outer measurement.
 5. The method of claim 1, whereinthe offset is determined based on a determination of the amount ofelectrical work that has been performed on the tire in substantiallyreal time.
 6. The method of claim 1, wherein the acquired electricalsignals corresponding to the amount of electrical work are parametersindicative of electrical power being consumed by an electric motordriving the iterative cuts.
 7. The method of claim 6, wherein theacquired electrical signals corresponding to the amount of electricalwork are measurements of an electric current being drawn by the electricmotor.
 8. The method of claim 1, wherein each of the iterative cuts isconducted at an in-feed that is the lesser of a predetermined in-feedand the offset.
 9. The method of claim 1, wherein a majority of theiterative cuts are performed by changing a radial position of thecutting device an equal amount relative to the central axis.